A hybrid vehicle includes an internal combustion thermal engine, which transmits torque to the driving wheels by means of a transmission provided with a gearbox coupled to a clutch, and at least one electric machine, which is electrically coupled to an electric storage system and mechanically coupled to the driving wheels.
The electrical power system of a hybrid vehicle includes a storage section, which is provided with at least one main automotive battery including a plurality of electrochemical cells which are coupled in series so that the voltage of the single cells is summed; the storage section works at an average voltage in the order of 200 Volts nominal. Furthermore, the electrical power system of a hybrid vehicle includes a section of traction which interacts with the electric machine and works at high voltage, in the order of 600-700 Volts nominal; the section of traction is coupled to the storage section by means of a two-way power electronic converter (i.e. that is either capable of absorbing electrical power from the storage section for powering the electric machine working as motor or capable of providing the electrical power generated by the electric machine working as generator to the storage section). Finally, the electrical power system of a hybrid vehicle includes a section of auxiliaries which powers all the auxiliary services of the vehicle requiring an electric supply and works at low voltage equal to 12 Volts nominal; the section of auxiliaries includes a buffer battery having a modest storage capacity (if compared to the main battery of the storage section) and is coupled to the storage section by means of a one-way power electronic converter which has the function of lowering the nominal voltage supplied by the storage section (200 Volts) to the nominal voltage (12 Volts) of the section of auxiliaries. In other words, the power electronic converter of the section of auxiliaries absorbs electrical power from the storage section at the power of 200 Volts for powering the auxiliary services and/or for recharging the buffer battery with a voltage of 12 Volts.
In modern hybrid vehicles, there are many auxiliary services which require electrical power and may absorb up to an overall high electrical power; consequently, the power electronic converter must be capable of providing a high electrical power (higher, even greatly, than 1000 Watts). However, a power electronic converter capable of providing high electrical power may be cumbersome and thus determines a non-negligible increase of total weight of the vehicle (currently, the tendency is to make the road vehicle as light as possible to reduce the energy consumption needed to move the road vehicle itself).
Patent application EP2056422A1, which is incorporated by reference, describes a discharge control system of a battery including a plurality of cells, each of which is coupled in series to the other cells and is provided with a bypass branch which is coupled in parallel to the cell and has an electronically controlled bypass switch. The bypass switches are controlled (i.e. opened and closed) to obtain a “balanced” discharge of the cells so as to exploit in greater measure the cells having higher electric charge (consequently a higher voltage at their terminals).